This invention relates to ultraviolet light absorbing polymer compositions, and more particularly, to polymer compositions comprising copolymers of 2-Hydroxy-5-acrylyloxyalkylphenyl-2H-benzotriazoles with one or more other monomers copolymerizable therewith, particularly acrylic monomers. This invention further relates to occular devices, particularly intraoccular lenses and contact lenses, prepared from such ultraviolet light absorbing polymers.
The absorption of radiation in the ultraviolet range by polymeric materials is a major cause of the light-induced degradation therein. It is standard practice to add a low molecular weight UV "stabilizer" to light-sensitive polymers to absorb the light in the destructive range or to quench the energy generated as a result of the excitation of the light-absorbing functional groups in the polymer.
Although low molecular weight UV absorbers or quenchers of various types are effective in inhibiting or retarding the destruction of the polymers to which they are added, their extractibility in various media and/or their volatility during the processing or fabrication of the polymers at elevated temperatures, provide a limitation on their utility.
This problem has been remedied to a considerable extent by the synthesis of copolymerizable monomers containing structural moieties capable of functioning as UV absorbers or quenchers. The copolymerization of such monomers results in the formation of copolymers with increased stability, i.e. resistance to degradation upon exposure to UV light with decreased extractibility and volatility. The addition of such copolymers to a suitable matrix polymer imparts these properties to the latter.
Examples of monomeric ultraviolet absorbers copolymerizable with acrylic monomers as disclosed in U.S. Pat. No. 4,304,895 for use in the preparation of UV absorbing hard contact lenses are ##STR1##
Similarly, the copolymerization of an allyl-2-hydroxybenzophenone with an acrylate ester such as methyl methacrylate is described in U.S. Pat. No. 4,310,650, and, the copolymerization of ethylenically unsaturated derivatives of 2,4-dihydroxybenzophenone with other vinyl type comonomers is broadly disclosed in U.S. Pat. No. 3,162,676.
UV absorbing lenses are particularly desirable for use by persons who have had their natural lenses surgically removed due to cataracts or some damage or natural deterioration of the lens. The visual correction of aphakia resulting from such lens removal requires the use of high plus corrective lens which may be in the form of specticles, contact lens or intraoccular lens.
A portion of incident light entering the eye is normally absorbed by various parts of the eye so that only the unabsorbed or transmitted portion strikes the retina. The incident light is, of course, comprised of the entire spectrum of wavelengths including the ultraviolet, visible and infrared.
The cornea preferentially absorbs that portion of the light with wavelengths up to about 300 nm. The crystalline lens preferentially absorbs the wavelengths from about 300 up to about 400 nm. There is also a characteristic absorption of the visible portion of the spectrum by other parts of the eye. The overall result of the various absorptions in the human eye is to permit the unabsorbed light to be transmitted to the retina, this light being defined by wavelength and intensity at each wavelength. It is apparent that in the aphakic eye, where there is no crystalline lens, light from 300 to 400 nm will be transmitted to the retina and that absorption in the visible range of the spectrum will also be changed to the extent that such visible light would have been absorbed by the crystalline lens. Accordingly, the entire spectrum of the light striking the retina in the aphakic eye is different from that in the normal eye.
Intraoccular lenses and hard contact lenses are presently produced from polymethylmethacrylate polymers which exhibit a combination of properties desirable for such products, particularly optical clarity, the capability of being cut and polished or molded to specific optical powers, and chemical inertness. UV absorbing lenses of PMMA are required to maintain these properties while achieving at least 85% absorption of light at 400 nm based on a polymer film thickness of 1 mm. In addition, the absorption must cut off sharply above 400 nm to avoid yellowing of the lens.
While the hydroxy benzophenones copolymerizable with acrylate monomers are effective UV absorbers and form chemically stable copolymers, relatively large amounts, i.e. 3 to 10% by weight, must be incorporated in the polymer to obtain 85% UV absorption at 400 nm and 1 mm thickness, and the compounds exhibit very broad absorption bands which extend into the visible range. Thus, polymers containing sufficient amounts of the benzophenone to provide effective UV absorption often have a significantly yellow cast.
It is accordingly an object of the present invention to provide a copolymer composition with improved UV absorption characteristics. It is a further object to provide a new UV absorbing composition which is copolymerizable with vinyl monomers. A yet further object is to provide a new composition of matter which when copolymerized with acrylic-type monomers is effective to absorb at least 85% of incident UV light at 400 nm and 1 mm thickness.
It is a further object to provide a new composition of matter which effectively absorbs UV light in the range of 300 to 400 nm but cuts off sharply above 400 nm.
These and other objects of the present invention will be apparent from the ensuing description and claims.